The invention relates to the manufacture of filter rods in general, and more particularly to improvements in a method and machine for making filter rod sections which can be used as or converted into mouthpieces for filter cigarettes, cigars or cigarillos. Still more particularly, the invention relates to improvements in a method and machine for making filter rod sections whose fillers consist of cellulose acetate or another suitable filamentary filter material.
A machine for the making of filter rod sections whose fillers consist of or contain filamentary filter material comprises a system of transporting rolls which draw a filamentary tow from a bale and stretch the tow during transport past a device which sprays droplets of liquid plasticizer (such as triacetin) against successive increments of the stretched (and preferably banded) tow. The tow is thereupon converted into a rod-like filler which is draped into a web of cigarette paper or other suitable wrapping material. The resulting rod is severed at regular intervals to yield a succession of discrete filter rod sections of desired length (e.g., six times unit length).
A drawback of many presently known filter rod making machines is that the quantity of filter material varies from section to section. Such fluctuations are due to the fact that the tow is not uniform, i.e., the width and/or density of the tow often varies from unit length to unit length or at irregular intervals. The density varies because the filaments of the tow are crimped and the crimp is not uniform. When a tow consisting of unequally crimped filaments is flattened or expanded (such operation is called banding) and is thereupon stretched during travel between transporting rolls which are driven at different peripheral speeds, the resulting spread out tow or layer often or invariably includes portions of greater and lesser density.
U.S. Pat. No. 3,399,606 to Molins discloses a filter rod making machine wherein the mass of the rod-like filler of filamentary filter material is monitored and the stretching or tensioning action of transporting rolls is changed when the monitored mass deviates from a desired value. Changing the tensioning action upon the filaments of the tow creates other problems, especially as concerns the predictability of treatments which follow the stretching step. Such treatments include the aforediscussed application of droplets of liquid plasticizer. Each change of the stretching action results in deviation of the quantity of plasticizer which is applied per unit length of the tow from a desired or optimum value.